Active noise control may be used to generate sound waves or “anti-noise” that destructively interferes with non-useful sound waves. The destructively interfering sound waves may be produced through a loudspeaker to combine with the non-useful sound waves in an attempt to cancel the non-useful noise. Combination of the destructively interfering sound waves and the non-useful sound waves can eliminate or minimize perception of the non-useful sound waves by one or more listeners within a listening space.
An active noise control system generally includes one or more microphones to detect sound within an area that is targeted for destructive interference. The detected sound is used as a feedback error signal. The error signal is used to adjust an adaptive filter included in the active noise control system. The filter generates an anti-noise signal used to create destructively interfering sound waves. The filter is adjusted to adjust the destructively interfering sound waves in an effort to optimize cancellation according to a target within a certain area called sound zone or, in case of full cancellation, quiet zone. In particular closely disposed sound zones as in vehicle interiors may result in more difficulty optimizing cancellation, i.e., in establishing acoustically fully separated sound zones, particularly in terms of speech. In many cases, a listener in one sound zone may be able to listen to a person talking in another sound zone although the talking person does not intend or desire that another person participates. For example, a person on the rear seat of a vehicle (or on the driver's seat) wants to make a confidential telephone call without involving another person on the driver's seat (or on the rear seat). Therefore, a need exists to optimize speech suppression between at least two sound zones in a room.